Until now, high-productive welding techniques, such as employed in the production of stainless steel tubes, have been carried out employing two or more non-consumable type electrodes in a single torch body, each electrode including a protective nozzle encircling the same. The arc established between each of the electrodes and the workpiece, by use of the above welding apparatus, is of the so-called open arc or TIG-arc type, that is, the wall of the nozzle has no influence on the arc so that an unrestricted or open arc is obtained. Due to the nature of the TIG-arc, the heat transfer from the electrode to the workpiece is effected through the upper side of the molten pool (added filler material), which results in a shallow penetration profile. Furthermore, welding with such a multi-electrode torch of the TIG type produces a wide molten weld pool and consequently there is a high consumption of energy per unit length of weld lead. Moreover, in a TIG-torch the electrode is rather unprotected, for which reason impurities from the surrounding air and from the motlen pool can easily be conducted into the inert gas surrounding the electrode. This gives an increased wearing of the electrode. When this wearing has reached a certain stage, the electrode must be taken out from the torch to be re-ground.